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Message-Id: <20240627055338.2186255-1-luyun@kylinos.cn>
Date: Thu, 27 Jun 2024 13:53:38 +0800
From: Yun Lu <luyun@...inos.cn>
To: vinicius.gomes@...el.com,
jhs@...atatu.com,
xiyou.wangcong@...il.com,
jiri@...nulli.us
Cc: netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: CPU stuck due to the taprio hrtimer
Hello,
When I run a taprio test program on the latest kernel(v6.10-rc4), CPU stuck
is detected immediately, and the stack shows that CPU is stuck on taprio
hrtimer.
The reproducer program link:
https://github.com/xyyluyun/taprio_test/blob/main/taprio_test.c
gcc taprio_test.c -static -o taprio_test
In this program, start the taprio hrtimer which clockid is set to REALTIME, and
then adjust the system time by a significant value backwards. Thus, CPU will enter
an infinite loop in the__hrtimer_run_queues function, getting stuck and unable to
exit or respond to any interrupts.
I have tried to avoid this problem by apllying the following patch, and it does work.
But I am not sure if this can be the final solution?
Thanks.
Signed-off-by: Yun Lu <luyun@...inos.cn>
---
net/sched/sch_taprio.c | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index a0d54b422186..2ff8d34bdbac 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -104,6 +104,7 @@ struct taprio_sched {
u32 max_sdu[TC_MAX_QUEUE]; /* save info from the user */
u32 fp[TC_QOPT_MAX_QUEUE]; /* only for dump and offloading */
u32 txtime_delay;
+ ktime_t offset;
};
struct __tc_taprio_qopt_offload {
@@ -170,6 +171,19 @@ static ktime_t sched_base_time(const struct sched_gate_list *sched)
return ns_to_ktime(sched->base_time);
}
+static ktime_t taprio_get_offset(const struct taprio_sched *q)
+{
+ enum tk_offsets tk_offset = READ_ONCE(q->tk_offset);
+ ktime_t time = ktime_get();
+
+ switch (tk_offset) {
+ case TK_OFFS_MAX:
+ return 0;
+ default:
+ return ktime_sub_ns(ktime_mono_to_any(time, tk_offset), time);
+ }
+}
+
static ktime_t taprio_mono_to_any(const struct taprio_sched *q, ktime_t mono)
{
/* This pairs with WRITE_ONCE() in taprio_parse_clockid() */
@@ -918,6 +932,7 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
int num_tc = netdev_get_num_tc(dev);
struct sched_entry *entry, *next;
struct Qdisc *sch = q->root;
+ ktime_t now_offset = taprio_get_offset(q);
ktime_t end_time;
int tc;
@@ -957,6 +972,14 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
end_time = ktime_add_ns(entry->end_time, next->interval);
end_time = min_t(ktime_t, end_time, oper->cycle_end_time);
+ if (q->offset != now_offset) {
+ ktime_t diff = ktime_sub_ns(now_offset, q->offset);
+
+ end_time = ktime_add_ns(end_time, diff);
+ oper->cycle_end_time = ktime_add_ns(oper->cycle_end_time, diff);
+ q->offset = now_offset;
+ }
+
for (tc = 0; tc < num_tc; tc++) {
if (next->gate_duration[tc] == oper->cycle_time)
next->gate_close_time[tc] = KTIME_MAX;
@@ -1210,6 +1233,7 @@ static int taprio_get_start_time(struct Qdisc *sch,
base = sched_base_time(sched);
now = taprio_get_time(q);
+ q->offset = taprio_get_offset(q);
if (ktime_after(base, now)) {
*start = base;
--
2.34.1
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